Biological fouling of circulating water in paper and pulp applications is a well documented problem. Biological growth in circulating water can foul pipelines, accelerate corrosion, attack wood, decrease heat transfer, block filters, cause imperfections in paper sheets, decompose sizing mixtures, and cause other process interferences. Algae, fungi, bacteria and other microorganisms found in circulating water are the underlying cause of such fouling. Several factors contribute to biological fouling and govern its extent. These factors include water temperature, water pH, aerobic or anaerobic conditions, the presence or absence of light, and the presence or absence of inorganic and organic nutrients either from air drawn into the system or from materials naturally occurring in the water or continuously supplied during plant operation.
Haloamines are well known biocides which effectively reduce, inhibit and/or control the proliferation of microorganisms that cause biological fouling in circulating water. Haloamines biocides are typically generated by combining a solution of active halogen donor species (e.g., hypochlorite) with an amine-containing composition (e.g., an ammonium halide solution). For example, U.S. Pat. Nos. 5,976,386 and 6,132,628 to Barak disclose the preparation of haloamine biocides from hypochlorite and various ammonium salts for use in treating liquids to inhibit the growth of microorganisms. In these patents, the hypochlorite solution is not generated in situ in the disclosed apparatus, but is instead drawn from a reservoir of pre-existing solution These active halogen donor species, such as hypohalites, are strong, corrosive oxidants, making them both difficult and dangerous to handle, especially in large quantities. Furthermore, these species degrade over time, resulting in active halogen donor species solutions having decreased potency and efficacy.
According to the present invention, haloamine biocides for use in treating liquids to reduce, inhibit and/or control the proliferation of microorganisms are prepared using an integrated apparatus comprising an electrochemical cell and a mixing chamber wherein the active halogen donor species is electrochemically generated upon demand in the electrochemical cell and subsequently mixed with an amine-containing composition in the mixing chamber. Thus, the degradation, handling, transportation and safety problems are minimized, since reservoirs of active halogen donor species solutions do not have to be filled and maintained according to the present invention. Additional advantages of the present invention include the wide range of compositional diversity possible, process flexibility, enhanced process control, and generation and shut-off of haloamine upon demand. Also, persons skilled in the art will recognize that the processes of the present invention can be used for microbial control in applications other than paper and pulp, e.g., disinfection of swimming pools, municipal water treatment, food treatment, and pharmaceutical applications.
Haloamines have been electrochemically generated in one step in an electrochemical cell. See e.g., C. Trembley et al., J. Chim. Phys., 90, 79 (1993) and C. Trembley et al., J. Chim. Phys., 91, 535 (1994). In “An Indirect Method for the Electrosynthesis of Monochloroamine,” B. V. Lyalin, et al., Russian Chem. Bull., 47, 1956 (1998), attempts to electrochemically generate monochloroamine (NH2Cl) in one step from ammonia in aqueous halide salt solution resulted in yields not exceeding 0.1%. Lyalin also discloses a two-step preparation of NH2Cl in only 50% overall yield. A solution of NCl3 in carbon tetrachloride is electrochemically generated from NH4Cl in one apparatus. This NCl3 solution is then mixed with ammonia in a second apparatus to generate NH2Cl. U.S. Pat. No. 3,776,825 to Jaroslav discloses aqueous monohaloamine solutions generated in an electrochemical cell charged with a halide salt solution and an amine containing compound for use in dental applications. Active halogen donor species are electrochemically generated and converted to hypohalite by introducing hydroxide. The hypohalite reacts in situ with the amine containing compound to form monohaloamine. None of the above references disclose a process for preparing haloamine biocide using an integrated apparatus comprising an electrochemical cell and a mixing chamber wherein the active halogen donor species is electrochemically generated upon demand.